1. Field of the Invention
The present invention relates to a method for preparing absolute alcohol.
2. Description of the Prior Art
In the conventional process for recovering ethanol from fermentation liquors, the dilute liquors obtained by fermentation of a suitable fermentable liquid material are passed through a beer still in which the ethanol and water are stripped from the liquor, usually by steam stripping, and the liquors are separated from nonvolatile dissolved solids. The solid free liquid product obtained from this step is only slightly enriched in ethanol. Thereafter, the ethanol/water mixture obtained is passed into a fractionator in which distillation of the liquid mixture occurs to produce an overhead which is about a 95% ethanol azeotrope and water is withdrawn as a bottoms product. In the conversion of the 95% ethanol-water azeotrope to absolute ethanol the azeotrope is distilled with benzene or a comparable hydrocarbon which breaks-up the azeotrope.
An analysis of the conventional alcohol distillation process shows that the total amount of energy required to obtain absolute ethanol from the fermentation liquor is at least 60% of the theoretical heating value of the ethanol product. This is a significant disadvantage for the large scale production of essentially water free ethanol for use as an ingredient in the production of gasoline-alcohol mixtures (commonly known as gasahol) which are to be used as motor fuels. If, in fact, ethanol is to find acceptable commercial utility as a motor fuel ingredient, the energy required to produce the substantially water free ethanol must be less than the energy that can be recovered from the combustion of the ethanol as a fuel. Moreover, the conventional distillation and recovery process is complicated since it requires three distinct processing steps which are the (1) beer still, (2) the fractionator and (3) the azeotropic distillation of the alcohol-water mixture with benzene or other similar drying agent. A need, therefore, continues to exist for a method by which substantially water free alcohol can be obtained using significantly less energy for the recovery of ethanol in comparison to conventional ethanol recovery procedures.